Preparation of 2-benzothiazolyl sulfene morpholide



nitecl States PREPARATION OF Z-BENZOTHIAZOLYL SULFENE MORPHOLIDE N Drawing. Application December 12, 1952, Serial No. 325,699

4 Claims. (Cl. 260-247.1)

This invention relates to rubber accelerators of the sulfenamide type. More particularly, it concerns the preparation of accelerators of the sulfenamide type. Still more particularly, it concerns the preparation of Z-benzothiazolyl sulfene morpholide.

In recent years rubber accelerators of this type have acquired great importance and numerous methods have been proposed for their preparation. None of these, however, has been completely satisfactory, particularly when applied to preparation of Z-benzothiazolyl sulfene morpholide. The main objection to these methods is failure to obtain the product in high yield and purity.

' One method, for instance, of preparing 2-benzothiazolyl sulfene morpholide is by condensation of N-chloromorpholine with sodium Z-mercaptobenzothiazole under alkaline conditions. This procedure, however, results in the production of by-product 2,2-dibenzothiazolyl disulfide as well as various highly colored impurities of obscure chemical nature. One elfort to eliminate this by-product formation was by use of an anhydrous organic solvent. This, however, created agitation difficulties and when solvent was employed in quantity suflicient to overcome this problem, there resulted commercially impractical reaction volumes.

More recently there has been described in application for United States Letters Patent Serial No. 227,510 filed May 21, 1951 by Robert C. Kinstler, the applicant herein, a method of preparing 2-benzothiazolyl sulfene morpholide in which these difiiculties are overcome and the product obtained in high yield and high purity. In general, it consists, as does the above described procedure, in condensation of N-chloromorpholine. Condensation, however, is carried out with the free Z-mercaptobenzothiazole rather than the sodium salt thereof. While this procedure gives a high purity product in excellent yield, it necessarily requires the presence of a substance, usually an amine, to serve as a hydrochloride acceptor. Although the formation, per se, of amine hydrochloride does not impair the yield or the quality of product, the relatively large volumes produced occupy substantial space, and reduce correspondingly the effective capacity of any given manufacturing equipment.

It is a primary object of this invention, therefore, to provide a method for the preparation of 2-benzothiazolyl sulfene morpholide. A further object of this invention is to improve the above described process by substantially reducing the formation of by-product hydrochloride while preserving the excellent features thereof. Such a method should, in general, follow the operational technique of the described procedure. Additionally, it should require neither unusual apparatus nor the use of large amounts of reagents that are expensive or cannot be regenerated.

This application involves the condensation of N-chloromorpholine with 2-benzothiazolyl disulfide. As such, it constitutes a continuation-in-part of copending application for United States Letters Patent entitled Preparation of 2-Benzothiazolyl Sulfene 227,510, filed May 21, 1951, by Robert C. Kinstler.

Morpholide, Serial No. k

Surprisingly, it has been found possible by the process of this invention to halve the by-product hydrochloride formation while still retaining all the desirable features of the process of the above described copending application. The manner in which these results are obtained involves the use of 2-benzothiazolyl disulfide in place of Z-mercaptobenzothiazole. That the objects are attained at all is particularly surprising inasmuch as previous use of the corresponding disulfide in various methods has not proved satisfactory. This is because only half of the disulfide molecule was utilized in formation of the product, while the other half resulted in by-product thiazolyl mercaptide. In surprising contrast, substantially quantitative yields are obtained in the present process and the difficult procedure necessary for separation of product from by-product thiazolyl mercaptide does not exist.

As in the process of the copending application, 2- benzothiazolyl sulfene morpholide is prepared herein by condensation of N-chloromorpholine. Condensation, however, is carried out by employing Z-benzothiazolyl disulfide rather than the free mercaptan and replacing half of the N-chloromorpholine with morpholine. These substances are brought together in an inert solvent in the presence of an acid acceptor. Condensation proceeds readily but may be further facilitated by mild heating if desired. On completion of the reaction, solid hydrochloride by-product is separated and product Z-benzothiazolyl sulfene morpholide recovered from the solvent.

As just described, 2-benzothiazolyl disulfide, TLchloromorpholine and morpholine in mol equivalents along with suflicient acid acceptor to neutralize evolved hydrochloride, are brought together in an inert organic solvent. The overall reaction may be represented by the following equation in which X represents the acid acceptor:

The same products, namely benzothiazolyl sulfene morpholide and by-product hydrochloride are obtained as in the process of the copending application. However, as shown by the equation, for each mol of Z-benzothiazolyl sulfene morpholide there is produced only /2 mol of hydrochloride, whereas when starting with the corresponding free mercaptan the ratio of product to by-product is 1:1.

Elimination of half of the bulky by-product hydrochloride has the elfect of doubling the productive capacity of any given equipment. This, in turn, results in sub stantial gains in efiiciency and econom of production. An additional advantage resides in the fact that the amount of N-chloromorpholine required to produce the same amount of Z-benzothiazolyl sulfene morpholine as when starting with the free mercaptan is halved. Since the entire disulfide molecule is utilized in formation of the sulfenamide, the problem, referred to above in description of previous use of disulfide, of separating product from by-product thiazolyl mercaptide, is eliminated. Preparation of N-chloromorpholine forms no part of this invention. One method which has been found to be very satisfactory, however, consists in chlorinating mor' pholine in situ in the same solvent to be used in the condensation reaction. Obviously, however, any other suitable method may be employed.

Choice of solvent in which condensation is carried out is limited only by the requirement that it be inert to the reactants under the mild reaction conditions. Various substances meet this requirement. Among those which may be mentioned as suitable solvents are, for example, chlorinated aliphatic hydrocarbons such as carbon tetrachloride and trichloroethylene, benzene and its homologues and their halogenated derivatives, thiophene, nitrobenzene and the like. Hydrocarbons and halogenated hydrocarbons of the benzene series, especially toluene and monochlorobenzene, have been found to be particularly suitable solvents.

Numerous materials may be employed to neutralize the hydrochloride evolved during the condensation reaction. However, amines, and particularly tertiary amines, have been found to be most efficient. Among those which may be used, for example, are triethylamine, N-ethylmorpholine, dimethylbenzylamine, tributylamine, pyridine, N-methylpiperidine, and the like. Morpholine itself is an efficient and particularly convenient amine to use. When morpholine is also used as the hydrochloride acceptor, the process will necessarily require at least two mols of morpholine.

After completion of the reaction, which may be accompanied by mild heating if desired, the solid byproduct hydrochloride is separated. This may be accomplished, for instance, by filtration or by any other suitable mechanical equivalent. The product, 2-benzothiazolyl sulfene morpholide, remains in solution. it may be recovered by any suitable method, such as by evaporation or steam distillation of the solvent.

A distinct advantage of the invention is the fact that the acceptor amine, whether it be morpholine or some other amine, may be conveniently recovered in a form readily reusable. This is accomplished by slurrying the amine hydrochloride in an anhydrous inert solvent and treating the slurry with ammonia. Neutralization rapidly takes place with liberation of the amine and formation of ammonium chloride. The latter is removed by filtration or other suitable means, leaving the amine in a pure form in solution. This solution may be directly chlorinated and recycled for reuse. If desired, recovery of the amine may be done in situ upon completion of the reaction. After removal of ammonium chloride, the product and regenerated acceptor amine may be readily separated.

The invention Will be further illustrated by the following examples. All parts are by Weight unless otherwise specified.

Example 1 To a mixture of 122 parts of N-chloromorpholine and 174 parts of morpholine in 1,000 parts of toluene is added 332 parts of 2-benzothiazolyl disulfide. The reaction mixture is stirred and cooled to keep the temperature at 30-45" C. Reaction is complete in approximately one hour. Resultant mixture is saturated with anhydrous ammonia and solid ammonium chloride thus produced separated. The toluene solution is then extracted with water to remove morpholine and steam distilled to remove toluene. 2-benzothiazolyl sulfene morpholide is obtained in essentially quantitative yield.

Example 2 To a mixture of 142 parts of N-chloromorpholine and 224 parts of morpholine in 1,000 parts of monochlorobenzene is added 385 parts of 2-benzothiazclyl disulfide. The reaction mixture is stirred and cooled to keep the temperature at 38-40 C. After 30 minutes reaction is complete and the mixture saturated with anhydrous ammonia. Solid ammonium chloride is filtered oflf. Resultant solution is extracted with water to remove morpholine and steam distilled to remove solvent. Product is obtained in a yield of 570 parts (98% of theory).

I claim:

1. A process of preparing 2-benzothiazolyl sulfene morpholide of high purity wherein 2-beuzothiazolyl disulfide is reacted directly with N-chloromorpholine and morpholine to form 2-benzothiazolyl sulfene morpholide and by-product hydrogen chloride which comprises the steps of: preparing an anhydrous solution of N-chloromorpholine and morpholine in an inert, volatile, organic solvent, the mol ratio of morpholine to N-chloromorpholine being about 2: 1; mixing Z-benzothiazolyl disulfide with said solution in amount substantially equimolar to said N-chloromorpholine; maintaining the mixture at reaction temperature until the reaction is substantially complete and byproduct hydrogen chloride is fixed as insoluble morpholine hydrochloride; and recovering Z-benzothiazolyl sulfene morpholide from the reaction mixture.

2. A process according to claim 1 in which the inert organic solvent is a hydrocarbon of the benzene series.

3. A process according to claim 2 in which the hydrocarbon is toluene.

4. A process according to claim 2 in which the hydrocarbon is monochlorobenzene.

References Cited in the file of this patent UNITED STATES PATENTS 2,045,888 Tschunkur et al June 30, 1936 2,261,024 Hanslick Oct. 28, 1941 2,271,834 Carr Feb. 3, 1942 OTHER REFERENCES Carr et a1.: J. of Org. Chem., vol. 14, pp. 921934. 

1. A PROCESS OF PREPARING 2-BENZOTHIAZOLYL SULFENE MORPHOLIDE OF HIGH PURITY WHERIN 2-BENZOTHIAZOLYL DISULFIDE IS REACTED DIRECTLY WITH N-CHLOROMORPHOLINE AND MORPHOLINE TO FORM 2-BENZOTHIAZOLYL SULFENE MORPHOLIDE AND BY-PRODUCT HYDROGEN CHLORIDE WHICH COMPRISES THE STEPS OF: PREPARING AN ANHYDROUS SOLUTION OF N-CHLOROMORPHOLINE AND MORPHOLINE IN AN INERT, VOLATILE, ORGANIC SOLVENT, THE MOL RATIO OF MORPHOLINE TO N-CHLOROMORPHOLINE BEING ABOUT 2:1; MIXING 2-BENZOTHIAZOLYL DISULFIDE WITH SAID SOLUTION IN AMOUNT SUBSTANTIALLY EQUIMOLAR TO SAID N-CHLOROMORPHOLINE; MAINTAINING THE MIXTURE AT REACTION TEMPERATURE UNTIL THE REACTION IS SUBSTANTIALLY COMPLETE AND BYPRODUCT HYDROGEN CHLORIDE IS FIXED AS INSOLUBLE MORPHOLINE HYDROCHLORIDE; AND RECOVERING 2-BENZOTHIAZOLYL SULFENE MORPHOLIDE FROM THE REACTION MIXTURE. 